This invention relates to a mounting arrangement for a vehicle powertrain.
A mounting arrangement for an engine must fulfil two main requirements. Firstly, the mounting must be able to support and control the powertrain under all operating loads, and secondly, the mounting must be strong enough to restrain the engine in the event of a crash. Various measures of crash worthiness are used for automobiles around the world, such as the European New Car Assessment Programme (Euro NCAP), with each measure defining a set of minimum safety requirements that a new vehicle must satisfy. Generally automobile manufacturers strive to exceed the minimum requirements so as to ensure that their vehicles score highly in each measure of crash worthiness.
In an automobile and many other types of vehicle, these requirements must be achieved while delivering an environment in line with the comfort targets for the vehicle in relation to the occupants and persons outside the vehicle. An engine is a significant source of noise and vibration in a vehicle and care must therefore be taken to ensure that the noise and modes of vibration of an engine are sufficiently isolated from the vehicle structure so as not to exceed the noise and vibration targets. Measurements of the noise and vibration characteristics of a vehicle are generally referred to as Noise, Vibration and Harshness (NVH) tests and comprise a mixture of objective and subjective tests on the noise and vibration developed by a vehicle.
In conventional mounting arrangements, an engine is supported by several rigid brackets coupled to the engine by means of flexible bushings, which are typically pan type bushings mounted onto the sides of the engine. The various forces generated between the engine and vehicle structure are distributed over the brackets, which work together to restrain the engine in the event of a crash. Each rigid coupling is generally stiff in all three dimensions so as to provide a secure connection between the engine and vehicle chassis and avoid any resonant couplings between the engine and vehicle. NVH performance can be achieved by appropriate tuning of the flexible bushings.
Such conventional engine mounting arrangements can provide the necessary strength but the rigid brackets add a significant amount of weight to the basic load bearing frame of an automobile. Furthermore, due to package constraints it is often difficult to attach to stiff regions of the body structure which can compromise the mount isolation, resulting in poor NVH performance of the system.
There is therefore a need for an improved powertrain mounting arrangement for vehicles which provides adequate NVH control and isolation.